1. Field of the Invention
The present invention relates to a medium, a method and a system for composite image formation. More particularly, the present invention relates to an image display medium capable of displaying a composite image including a display image and a latent image, and a preparation method and a generation system for preparing composite display image data.
2. Description of the Related Art
Recent technological advances in various fields such as image forming and image processing have made it harder to distinguish an original from a duplicate of the original.
In one example, an attempt is made to distinguish an original from a duplicate by using an image processing apparatus capable of detecting a counterfeit or alteration of an image on ordinary paper. The image processing apparatus sequentially generates a character image from a character code, a background pattern from character information, and a composite image including the character image and the background pattern and sends the composite image to a thermal printer so that the composite image is printed. Since the background pattern is formed in such a manner as not to be in contact with the character image, deletion from and addition to the original can be easily identified.
Other examples attempt to distinguish between an original and a duplicate of the original by using ground tint patterns, which are visible in the original while invisible in the duplicate or vice versa. The original includes a display image and a latent image. Each of the display image and the latent image has a halftone dot image with a different density. For example, at least one area of the latent image includes relatively large dots while at least one area of the display image includes relatively small dots. When the original is copied, the large-dot area of the latent image becomes clearly visible while the small-dot area of the display image is omitted (i.e., becomes invisible), thus making it possible to determine if the image is an original or a duplicate.
However, the latent image has to be positioned across the entire page of the original to form a visible area and/or an omitted area with relatively large-sized characters, which limits the number of characters that can be displayed. Specifically, only simple words such as “COPY PROHIBITED” can be used. In addition, such characters cannot be used as text characters.